This is a proposal to study the molecular genetics of mating type and sexual development in Schizophyllum commune. This fungus has four multiallelic, mating-type loci, A alpha, A beta, and B beta loci. Representative alleles of each locus will be cloned and sequenced. Regions that are essential for A function will be identified, the number of complementation groups in each locus will be determined and the expression of genes in these loci will be studied. Attempts will be made to identify the gene products and determine their cellular location. Mutations that alter self-nonself recognition of the alleles will be isolated and analyzed. A mutant hunt will be made to identify genes regulated by the A alpha and A beta loci. At present nothing is known about the number of genes at each locus, the gene products, and the differences and similarities between alleles. The proposed studies are expected to answer these questions and they will begin to address the question of how the A loci regulate genes in the A-specific pathways of sexual development. Information obtained in this study of Schizophylum will also contribute to understanding the nature of multiallelic genes and self-recognition in other organisms.